Abstract
A new analytical quasistationary diffusion model of hydrogen and carbon diffusion in Fe-H-C-i austenite/austenite type weldments is presented. The new model extends the experimentally verified and published quasistationary Fe-C-i model of hydrogen. The diffusion rate of hydrogen is of many orders higher than the substitutional elements diffusion rate and of also several order higher than carbon diffusion rate. Thus, the redistribution of hydrogen imitates the redistribution of carbon and distribution of substitution elements, while the redistribution of carbon imitates only the distribution of substitution elements. The new model is presented in the form of a system of the analytical relations. Using the thermodynamic, diffusion, and phases data, it is possible, by means of this relations, to calculate the i-elements, carbon and hydrogen concentration curves in the austenite/austenite steel structure weldments at different temperature and time of annealing. The limiting conditions of the presented quasistationary model in the above-mentioned welding joints are discussed.

Key words
steel weldments, dissimilar Fe-H-C-i austenite, diffusion H-C, hydrogen redistribution, quasistationary model, thermodymanic data, hydrogen curves

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